A long lifetime nuclear reactor of the type on which the present invention is an improvement is disclosed in U.S. Pat. No. 3,252,867 (Conley). Such heterogenous reactors have been used as power producing reactors in a number of locations and for example, have been constructed using a seed of highly enriched uranium-235 and a blanket of natural uranium.
A Light Water Breeder Reactor (LWBR) has been built using a seed of uranium-233 and a blanket of thorium-232. Both of these heterogeneous nuclear systems have utilized seed-blanket constructions wherein the fissile (seed) and fertile (blanket) nuclear fuels are segregated in a radial fashion throughout the core. This construction has resulted in radial core regions of high power density which lie adjacent to radial core regions of low power density, thereby producing relatively high radial power peaking, and hydraulic orificing has been required to balance the thermal performance of the core.
The Conley reference mentioned above specifically concerns a seed-blanket reactor wherein a plurality of seed regions are disposed in radially spaced relationship with a blanket region surrounding each of the seed regions. Other patents of possible interest here include U.S. Pat. Nos. 2,992,174 (Edlund et al); 3,211,621 (Creagan); 3,396,078 (Visner); 3,660,227 (Ackroyd et al); 3,671,392 (Beaudoin et al); 3,960,655 (Bohanon); and 4,257,847 (Gibby et al). These patents disclosed various arrangements of the fertile and fissile fuel materials in the fuel element of breeder reactors. For example, the Beaudoin et al patent discloses a light-water breeder reactor including a specific axial arrangement of fertile and fissile fuel materials and the Gibby et al patent discloses a nuclear breeder reactor including a particular arrangement of fertile and fissile fuel material within the reactor core. The Creagan patent discloses a breeder or converter type neutronic reactor including a particular arrangement of fissile and fertile fuel.